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Steve G.
Steve G., Electrical Engineer
Category: Electrical
Satisfied Customers: 17726
Experience:  Spent 20 years as an Electrical Engineer, designing electrical plans and specifications.
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I am replacing a 400W HPS with a multi volt high bay flouresent.

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I am replacing a 400W HPS with a multi volt high bay flouresent. The wires that went to the HPS were both black,can I hook the new white wire to the black one? Is one of the black wires working as a common?
Hello there and welcome to Just Answer. My name is XXXXX XXXXX I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.

Now..what voltage is your lighting? 460? 277? 240? 120?

Please let me know so that we can continue.

Customer: replied 3 years ago.

The voltage for the old light is 240 I believe, but there is 3 phase in this building so would that change it to 277?

It could be 240, it could be 277.

Either way, you have two wires and assuming that your replacement fixture is rated correctly, you can simply hook it up to the two wires poking out of the ceiling.

Make sure you ground the fixture to the box and the ground wire.

I'll be here if you need further help with this issue. Please let me know.

Customer: replied 3 years ago.

So I can hook up the new fixture which is a florescent mutli volt ballast which has a black,white, and green, to the existing 2 black wires that was coming out of the conduit that went to the existing 400w HPS light?

If your existing fixture was rated for 240V and your new one is rated for 240V then connect it up. There is no other solution of combination of wires here - you have to select two wires from three and one of those is a ground which leaves you with two.

You will be fine. :)

Customer: replied 3 years ago.

Would you know why there is not a neutral that would run with both of the black wires?

You are assuming that a wire is a neutral because it is white. This is not always the case. There are many scenarios in electrical engineering where there is no neutral at all. My 240V water heater in my home has no neutral.

May I suggest that you get a Fluke meter and measure the voltage from each wire to ground and from black wire to black wire? Give me the results and I'll tell you if you have a neutral.

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